One type of composite structure used in a variety of applications comprises a core sandwiched between a pair of composite facesheets, sometimes referred to as a sandwich structure. Where the core includes multiple core details, such as multiple core segments joined together, the structure may be referred to as a “core blanket”. The core in these structures may be formed of any of various materials including, but not limited to honeycombs, foams and balsa, to name only a few. The facesheets may be formed from multiple laminated plies of a fiber reinforced resin.
Inconsistencies may sometimes occur within localized areas of the facesheets of these sandwich structures. For example, a facesheet may contain a void, a dent or a porosity that may occur at the time the facesheet is manufactured or later during the service life of the sandwich structure. For instance, a facesheet impacted by an object may cause a localized disbond or crack occurring in one or more plies of the facesheet. Unless arrested, a disbond or crack may spread or propagate to areas outside of the local impact area.
One solution to the problem involves the inclusion of substructures within the sandwich to limit the propagation of inconsistencies, however substructures may be relatively expensive to manufacture and assemble, and may add additional weight to the sandwich structure. In addition, known substructure solutions are specifically designed to either limit propagation of disbands or cracks, but may not limit both. It may be possible to combine multiple substructure designs in order to arrest the propagation of both disbonds and cracks, however the use of multiple substructures may lead to an overall composite structure design that exceeds target weight specifications. Another solution to the problem is to limit the operating strain applied to the sandwich structure, and perform periodic visual checks on the integrity of the structure, however this approach may not be practical in some applications where the operating strains placed on the sandwich structure cannot be limited, and/or predicted.
Accordingly, there is a need for a sandwich structure having a lightweight but robust core capable of reducing or arresting the propagation of irregularities that may occur in the structure, particularly as a result of object impacts.